In recent years, a technique called a radio frequency identification (RFID) used in an RF tag, a non-contact type IC card, and the like has spread. For example, an RF tag includes an antenna therein, and performs near field communication with a dedicated reader/writer using a weak radio wave.
Among RF tags, there is an RF tag having a function of a reader/writer communicating with another RF tag as well as a function of an RF tag communicating with a dedicated reader/writer. Such an RF tag operates as an RF tag or a reader/writer according to a use state.
The present applicant has previously proposed a communication device having a function of an IC card (RF tag) and a function of a reader/writer (for example, see Patent Document 1). FIG. 1 illustrates a configuration of a communication device 1 having both functions of an RF tag and a reader/writer.
As illustrated in FIG. 1, the communication device 1 includes an antenna circuit 11, an integrated circuit 12, a host controller 13, a power source 14, an oscillating circuit 15, and a crystal oscillator 16. The antenna circuit 11 includes a coil 31 and a capacitor 32 and forms a parallel resonant circuit. The power source 14 supplies the integrated circuit 12 and the host controller 13 with electric power. The oscillating circuit 15 generates a carrier of a frequency (13.56 MHz) corresponding to a vibration frequency of the crystal oscillator 16.
The integrated circuit 12 modulates transmission data according to control of the host controller 13, and transmits a modulated signal obtained by the modulating to a communication destination through the antenna circuit 11. Further, the integrated circuit 12 receives a modulated signal from a communication destination through the antenna circuit 11 according to control of the host controller 13, and demodulates the modulated signal.
The integrated circuit 12 includes a control unit 51 that controls respective units, a non-volatile memory 52 that appropriately stores various kinds of data, a data input circuit 53 that receives transmission data, and a data output circuit 54 that outputs reception data The control unit 51 includes a mode control unit 71 and a communication control unit 72. The mode control unit 71 controls switching operations of a switch 55 and a switch 56 according to control of the host controller 13. The communication control unit 72 not only controls an input and output of the transmission data and the reception data but also performs various kinds of processes on the data.
Here, an operation mode of the communication device 1 includes a reader/writer mode in which the communication device 1 operates as a reader/writer and a tag mode in which the communication device 1 operates as an RF tag. To this end, the integrated circuit 12 is provided with a transmitting circuit 57 serving as a circuit for a reader/writer function, a transmitting circuit 61 serving as a circuit for an RF tag function, and a receiving circuit 63 serving as a circuit for both functions.
When an operation is performed the reader/writer mode, the transmitting circuit 57 performs Amplitude Shift Keying (ASK) (hereinafter, referred to as an “ASK modulation”) on the transmission data supplied from the communication control unit 72 according to a carrier generated by the oscillating circuit 15. At this time, in order to perform the ASK modulation through the transmitting circuit 57 while generating the carrier through the oscillating circuit 15, it is necessary to compulsorily change a level of the carrier while driving the carrier at low impedance. To this end, transmitting buffer circuits 58 and 59 are provided so that the carrier can be driven at the low impedance. As a result, the modulated signal obtained by the ASK modulation is transmitted to the RF tag of the communication destination through a filter circuit 60 and the antenna circuit 11.
When an operation is performed in the tag mode, the transmitting circuit 61 performs load modulation on reply transmission data supplied from the communication control unit 72 according to a clock signal extracted by a clock extracting circuit 62, and applies the modulated data to the coil 31 of the antenna circuit 11. As a result, the reply transmission data is transmitted to the reader/writer of the communication destination.
The receiving circuit 63 is a circuit that is used in both operation modes of the reader/writer mode and the tag mode. When an operation is performed in the tag mode or the reader/writer mode, the receiving circuit 63 receives a modulated signal transmitted from a communication destination through the antenna circuit 11 and the filter circuit 60, demodulates the modulated signal, and supplies reception data obtained by the demodulating to the communication control unit 72.
As described above, the communication device is configured to have both functions of the RF tag and the reader/writer.